Faunus ater

Faunus ater is a species of brackish water snail with an operculum, an aquatic gastropod mollusk in the family Pachychilidae. Faunus ater is the only species within the genus Faunus. The distribution of Faunus ater includes: The periostracum is thick, and the color of the periostracum is dark brown or black. The shell has about 20 whorls. The apical whorls may be eroded in older snails. The aperture is ovate and white. The shell is unique among Cerithioidea, because it has two deep sinuses: an anal sinus which is close to the suture and an anterior sinus more forward in the aperture. The height of the aperture is about one-fifth of the height of the shell. The height of the shell is usually 50–60 mm, but can be up to 90 mm. The operculum is oval, corneous and dark brown in color. The snail has a broad snout. The radula is large and is located in a correspondingly large buccal mass. This snail lives in slightly brackish water. It has also been reported from freshwater. It is the only pachychilid species that lives in brackish water; the other species in the family are freshwater snails.